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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        // 第三方变量交换
        let a=1;
        let b=2;
        let temp;
        temp=a;
        a=b;
        b=temp;
        console.log(a,b);

        // 
        let num1=10;
        let num2=20;
        // 30
        num1=num1+num2;
        // 10
        num2=num1-num2
        // 20
        num1=num1-num2;
        console.log(num1,num2);
    </script>
</body>
</html>